Biogas production by anaerobic co-digestion of sugarcane biorefinery byproducts: Comparative analyses of performance and microbial community in novel single-and two-stage systems

Food waste biorefinery towards circular economy in Australia

Staggering amounts of food waste are produced in Australia, and this review provides food waste based biorefinery opportunities in moving towards a circular economy in Australia. The current food waste scenario in Australia including an overview of primary food waste sources, government regulation, and current management practices is presented. The major food waste streams include fruit and vegetable (waste from wine grapes, citrus, apple, potato, and tomato), nuts (almond processing waste), seafood (Fish waste), dairy whey, sugarcane bagasse, and household and businesses. The composition of these waste streams indicated their potential for use in biorefineries to produce value-added products via various pathways combining direct extraction and biological and thermochemical conversion. Finally, the efforts made in Australia to utilize food waste as a resource, as well as the challenges and future directions to promote the development of concrete and commercially viable technologies for food waste biorefinery, are described.

Two-stage biohydrogen and methane production from sugarcane-based sugar and ethanol industrial wastes: A comprehensive review

The transition to renewable energy sources is crucial to ensure a sustainable future. Although the sugar and ethanol industries benefit from this transition, there are untapped opportunities to utilize the waste generated from the sugar and ethanol process chains through two-stage anaerobic digestion (TSAD). This review comprehensively discusses the utilization of various sugarcane-based industrial wastes by TSAD for sequential biohydrogen and methane production. Factors influencing TSAD process performance, including pH, temperature, hydraulic retention time, volatile fatty acids and alkalinity, nutrient imbalance, microbial population, and inhibitors, were discussed in detail. The potential of TSAD to reduce emissions of greenhouse gases is demonstrated. Recent findings, implications, and promising future research related to TSAD, including the integration of meta-omics approaches, gene manipulation and bioaugmentation, and application of artificial intelligence, are highlighted. The review can serve as important literature for the implementation, improvement, and advancements in TSAD research.

Enhancing Biobased Volatile Fatty Acids Production from Olive Mill Solid Waste by Optimization of pH and Substrate to Inoculum Ratio

The pH and substrate-to-inoculum ratio (S/I) are important parameters in the anaerobic fermentation of agroindustrial residues, and therefore the optimization of these two parameters is needed for a stable, efficient, and sustainable reactor operation. In this work, the parameters pH (5–9) and S/I (0.5–3 gVS gVS−1) were optimized to produce biobased volatile fatty acids (VFAs) from hydrothermally pretreated olive mill solid waste (HPOMSW). The response variables evaluated in the Doehlert design were total VFAs concentration (tVFAs) (mg L−1) and amounts (%) of isobutyric, butyric, isovaleric, and valeric acids on the VFAs profile. The pH was the variable that most influenced the mixed culture fermentation of HPOMSW, proving to be a key parameter in the process. Microbial community analyses of conditions 1 (S/I = 3 gVS gVS−1 and pH = 7) and 4 (S/I = 1.13 gVS gVS−1 and pH = 5) showed that Proteobacteria and Firmicutes accounted for more than 87% of the total microorganisms identified for both conditions. In addition, the second-order model best fitted the experimental data for the VFAs production at the desirable condition (S/I = 3 gVS gVS−1 and pH = 8).

A Review of Basic Bioinformatic Techniques for Microbial Community Analysis in an Anaerobic Digester

Biogas production involves various types of intricate microbial populations in an anaerobic digester (AD). To understand the anaerobic digestion system better, a broad-based study must be conducted on the microbial population. Deep understanding of the complete metagenomics including microbial structure, functional gene form, similarity/differences, and relationships between metabolic pathways and product formation, could aid in optimization and enhancement of AD processes. With advancements in technologies for metagenomic sequencing, for example, next generation sequencing and high-throughput sequencing, have revolutionized the study of microbial dynamics in anaerobic digestion. This review includes a brief introduction to the basic process of metagenomics research and includes a detailed summary of the various bioinformatics approaches, viz., total investigation of data obtained from microbial communities using bioinformatics methods to expose metagenomics characterization. This includes (1) methods of DNA isolation and sequencing, (2) investigation of anaerobic microbial communities using bioinformatics techniques, (3) application of the analysis of anaerobic microbial community and biogas production, and (4) restriction and prediction of bioinformatics analysis on microbial metagenomics. The review has been concluded, giving a summarized insight into bioinformatic tools and also promoting the future prospects of integrating humungous data with artificial intelligence and neural network software.

Aerobic post-treatment of effluent from anaerobic reactors fed with residues from 1G and 2G sugarcane biorefineries

This study aimed to evaluate an activated sludge system as a post-treatment step of anaerobic effluents from the co-digestion of sugarcane vinasse and hemicelluloses hydrolysate. The system consisted, initially, of a two-stage anaerobic system followed by a continuously fed activated sludge, all in bench scale. After adaptation of aerobic microorganisms to effluent conditions, the anaerobic digestion was conducted in a single-stage anaerobic reactor, increasing the influent organic loading rate (OLR) of activated sludge from 0.73 to an average of 2.36 gCOD/L·day. Under optimal conditions (12-h hydraulic retention time [HRT]), a 62 ± 9% efficiency was observed on the aerobic post-treatment, resulting in effluent chemical oxygen demand (COD) of 414.3 ± 95 mg/L. Overall efficiency of the combined system (anaerobic + aerobic) averaged 88 ± 3%. Influent and effluent characteristics were then analyzed by Folin-Ciocalteau method, UV-Vis spectrophotometry, and gas chromatography-mass spectrometry (GC-MS) for identification of potentially toxic and recalcitrant compounds. Compounds that absorb light within the visible spectra were well removed by the combined treatment system. Most compounds identified by GC-MS in the influent were completely removed by aerobic microorganisms. Saturated fatty acids such as adipic acid, hexadecanoic acid, and octadecanoic acid were observed in the final effluent, as well as other potentially toxic compounds such as stigmasterol, di-isobutyl phthalate, and benzene. Activated sludge proved to be an efficient post-treatment for anaerobic co-digestion, able to cope with changes of anaerobic effluent quality and providing a final effluent of stable organic load. However, phenol removal was not efficient and further studies could be performed to optimize its degradation. PRACTITIONER POINTS: Conventional activated sludge with a 12-h HRT was capable of handling significant OLR variation, providing a final effluent with lower and stable COD concentration. Glucose addition for carbon supplementation was necessary during the start-up of activated sludge. Compounds that absorb light within the visible spectra were mostly removed by the combined (anaerobic-aerobic) treatment system. Most potentially toxic compounds were well removed in the post-treatment system. Saturated fatty acids, VFA, phenols, and low molecular weight aromatic compounds remained in the final effluent.